Grafting of vinylimidazole into air-irradiated polymer films—2. Grafting into polyethylene

Abstract

Polyethylene films exposed in air to gamma-rays were heated under vacuum with vinylimidazole (VI) both in bulk and in aqueous solutions. It was found that the limiting extent of grafting increases linearly with monomer concentration in water up to 90% (molar), but that a much faster reaction takes place in bulk where the grafting yields reach extremely high values. The reaction was studied at temperatures ranging from 70 to 90°. Over all activation energies were 109 ± 10 kJ/mol in 50% aqueous solutions and 144 ± 10 kJ/mol in bulk. The limiting grafting yields observed in bulk increase with the dose of irradiation according to a second order law. The results are compared with those obtained in part 1 of this work on similar grafting into Teflon-FEP films. Some of the observed differences are related to the different nature of initiating centres: trapped peroxy radicals in Teflon-FEP as opposed to hydroperoxides and diperoxides in polyethylene. However, a complex reaction also occurs when VI is contacted with peroxides as was already reported in studies on the polymerization of VI by benzoyl peroxide.